Continuous sheet extrusion apparatus



Jan. 28, 1964 I J. A. CHAMBERS ETAL 31-19148 CONTINUOUS SHEET EXTRUSION APPARATUS Filed March 14, 1961 4 Sheets-Sheet l l WIWI/ I -22- I F l20 v 24 32 l 343- .ad gf/,5722 ef/M. MadJo/f 5% ifa/waar 4 Sheets-Sheet 2 Ef; 7J

J. A. CHAMBERS ETAL VCONTINUOUS SHEET EXTRUSION APPARATUS lllllll "..lhllhlhnllh H HUND Jan. 28, 1964 Filed March 14. 1961 Jan- 28, 1964 J. A. CHAMBERS rs1-AL 3,119,148

CONTINUOUS SHEET EXTRUSION APPARATUS f ff L Jan. 28, 1964 J. A. CHAMBERS ETAL CONTINUOUS SHEET EXTRUSION APPARATUS 4 Sheets-Sheet 4 Filed March 14. 1961 illib Patented Jan. 28, i964 i ice CONTINUGUS SHEET EXTRUSIUN APPARATUS .lack A. Chambers, Manhattan Beach, and Leslie A.

Woodson, Los Alamitos, Calif., assignors to W. S.

Shamban Company, Culver City, Calif., a corporation of California Filed Mar. 14, 1961, Ser. No. 95,705 13 Claims. (Ci. 18-12) This invention relates to a wall structure for confining a iiuid under pressure and, more particularly, a wall structure including a relatively wide wall that tends to bow outward under the fluid pressure, the invention being directed specifically to anti-deiiection means to resist such a tendency.

While the invention is broadly applicable for its purpose, it has been initially embodied in a wall structure for confining heated plastic material under high pressure. The description herein of this embodiment will provide adequate guidance for those skilled in the art who may have occasion to apply the same principles to other specie purposes.

In the initial embodiment of the invention, a Wall structure forms a passage of relatively great width and relatively small thickness dimension for the purpose of forming and extruding a continuous relatively Wide sheet of tetrauoroethylene (TFE) resin. Successive increments of the raw TFE material are rammed into the entrance of the passage and heating elements mounted on the wall structure of the passage transfer heat through the wall structure to the confined TFE resin to raise the temperature of the resin to a sintering temperature above 600 F. The ramming of the successive increments into the forming passage is opposed by high frictional resistance to movement of the plastic material through the passage with the consequence that the confined material is subjected to an exceedingly high pressure. The pressure may range in excess of 500 p.s.i.

Since the side walls of the passage are relatively wide planar walls which are interconnected only at their opposite side edges, there is a tendency for the walls to bow outward under the fluid pressure. Even when the side walls are relatively thick steel plates, this tendency, if not counteracted, results in the final sheet product having opposite convex faces instead of accurately planar faces. The bowing tendency is further aggravated because heat is transferred through the passage walls to the confined plastic material with the consequence that a temperature differential is created through the thickness of each wide side plate of the wall structure, the lower temperature being, of course, at the inner surface of the side plate. Such a temperature differential creates an additional tendency for a side plate to bow outward.

The present invention meets this problem by applying an opposing force to a side wall of the passage to tend to bow the side wall inward in opposition to the outwardly bowing tendency of the side wall. In the preferred practice of the invention the counteracting force is provided by an anti-deflection member which functions as a reinforcing member. A reinforcing member is connected to each of the wide walls of the wall passage structure with the reinforcing member extending transversely thereof and an opposite temperature differential is created in the reinforcement member whereby the reinforcement member tends to bow inward in opposition to the outward bowing tendency of the side wall. The invention further teaches the use of adjustable means to create the desired counteracting temperature differential in combination with means to sense and indicate the magnitude of the temperature ditferential for control purposes.

In another practice of the invention, force created by hydraulic means or by other suitable mechanical means is applied to each relatively wide wall of the passage structure to counteract the outward bowing tendency of the wide side wall. For this purpose a hydraulic ram may be employed with suitable valve means for varying the magnitude of the counteracting force.

The invention further teaches the use of a servo loop for automatic control of the counteracting force. For this purpose means is provided to sense outward bowing of the wide side wall of the passage structure and variable means responsive to the sensing means applies the counteracting force. The sensing means may be a strain gage which senses outward bowing of the side passage wall.

In an embodiment of the invention in which the counteracting force is obtained by creating an opposing temperature differential in a reinforcing member, the temperature differential is automatically controlled by means that is responsive to the sensing means. In an embodiment of the invention in which hydraulic means is employed to apply the counteracting force, the valve means for controlling the hydraulic means may be responsive to the sensing means.

The features and advantages of the invention may be understood by reference to the following detailed description and the accompanying drawings. In the drawings, which are to be regarded as merely illustrative:

FIG. 1 is a vertical sectional View of an apparatus for extruding a relatively wide TFE sheet, the apparatus incorporating a selected embodiment of the present invention;

FIG. 2 is a side elevation of the same apparatus;

FIG. 3 is a transverse sectional view of the same apparatus;

FIG. 4 is a view partly in plan and partly in section, the section being taken along the broken line 4-4 of FIG. 1;

FIG. 5 is a fragmentary perspective view showing the construction of a clamp bar for anchoring a cooling tube against the wall structure;

FIG. 6 is a fragmentary side elevation showing how thermocouples may be incorporated in an anti-deflection plate to sense the temperature differential therein;

FIG. 7 is a side elevation of a cooling member that is mounted on the outer edge of an anti-deliection plate;

FIG. 8 is a wiring diagram showing variable heating circuits for creating temperature differentials on opposite sides of a passage structure and showing thermocouples connected to a recording pyrometer to sense the temperature differentials in the anti-deiiection plates that are created by the heating circuits;

FIG. 9 is a wiring diagram showing how variable heating circuits for creating temperature differentials on the opposite sides of a passage structure may be automatically controlled in response to means for sensing outward bowing of the side walls of the passage structure;

FIG. 10 is a schematic plan View showing how hydraulic rams may be used on opposite sides of a passage structure to apply force to counteract the outward bowing tendency of the passage structure walls, the hydraulic rams being controlled automatically by strain gages that sense outward bowing of the passage structure; and

FIG. l1 is a fragmentary sectional view taken as indicated by the line 1li-ll of FIG. 10.

The appanatus shown in FIGS. l-S is employed for continuously producing a relatively l'Wide TFE resin sheet, genenally designated S. The sheet may be, for example, from 1A" to l" thick Iand may be fnom 12" to 40 wide or wider. To serve its purpose, the apparatus comprises Ia passage structure ifnominig ea stnaight passage 20 of the .desired cross sectional configuration, the passage dime-nsions being slightly greater than the desired dimensions of the sheet to allow for the `final shrinkage as the formed sheet cools to room temperature.

The passage structure comprises an upper heating stage structure providing successive heating zones A and B and a lower cooling stage structure providing the next succeeding cooling zones C and D. The formed sheet S hangs vertically downward from the lower discharge end of the cooling stage structure.

In the construction shown, the upper heating stage structure comprises two thick metal side plates 22 and two spacer end plates 24, the assembly being interconnected by suitable fasteners such as bolts 25. An initial feeding zone at the entrance to the forming passage 20 is provided by a structure that forms a continuation of the passage and includes a pair of spaced feed plates 2-6 mounted on spaced bars 23. The naw plastic material is fed to the forming passage 20 from the `upper surfaces of the feed plates 26 and a reciprocating nam 301 forces successive increments of `the plastic material into the entrance of lthe forming passage 2G.

The creation of heat in each of the two heating zones A and B is accomplished by a pair of transverse electrical heating elements 32 on each side of the Wall structure. Each pair of heating elements 32 is mounted on a. thick aluminum plate 34- itliat is mounted on -the corresponding side plate 22 of the pass-age structure. The aluminum plate by virtue of its high thermal conductivity distributes heat uniformly from the two heating elements. A thermocouple 35 extends into each of the two side plates 22 to sense the local temperature of the wall structure. The second heating zone B comprises the sarne arrangement of a pair of heating elements 35 mounted on an aluminum plate 38 on each side of the passage structure with a pair of thermocouples 40 to sense the local temperatures. Heat fiow from Zone A to zone B is retarded by the presence of relatively wide and relatively deep external ltransverse grooves 42 in the two side plates 22.

The lower cooling stage structure is of the same general construction `and includes a pair of heavy side plates 44. The cooling stage C holds the material in the passage 20 at a temperature substantially below the ternperature in the heating zones A and B but substantially above room temperature. For this purpose the heating stage C has a pair of transverse heating elements 45 mounted ion the opposite side plates 44 with a pair of thermocouples 46 to sense the local temperatures. The passage structure may be further heated by heating elements 48 on ythe opposite side edges of the passage structure.

It may be readily appreciated that with the pressure of the traveling resin in the passage 20 at a magnitude on the order of 600 p.s.i. the side plates 22 that determine the thickness `and configuration of the sheet S tend to bow outward under the pressure. It may be further appreciated that since `the traveling resin is raised to a temperature on the order of 600 F. by the heating elements 32 and 36, a temperature gradient exists through the thickness of each of the side plates to create a temperature differential with the higher temperatures towards the outer faces of the side plates. This temperature differential that is an inevitable consequence of heating the resin through the side plates causes the side plates to bow outward in `the same manner as the fluid pressure of the confined resin.

In the first embodiment of the invention the tendency of the two side plates 22 to bow outward is resisted and completely counteracted by what may be ltermed a pair of anti-deflection members 50 which are mounted on opposite sides `of the entrance to the pasage 2?. Each of the anti-deflection members f) is in the form of a heavy horizontal plate of substantial width which is suitably connected at its inner edge to the corresponding side plate 22. As indicated in FIGS. l and 4, each of the antideflection plates 50 may be mounted on the upper edge of the corresponding side plate 22 and may be firmly attached vto `the side plate by spaced heavy screws 52.

-In accord with the `teaching of the invention, a temperature differential is created in each of the anti-deflection plates that tends to cause the anti-deflection plate to bow horizontally inward to countenact the outwardly bowing tendency of the two side plates 22. It will be apparent Ito those skilled in the art that various arrangements may be employed to create the desired counteracting temperature differentials in the two anti-deflection plates 50;

The present embodiment of the invention takes advantage of the fact that since the inner edge of an antidefiection member 50 is attached to the corresponding side plate 212, the anti-deflection plate is heated by conduction Ifrom the side plate with the consequence that a temperature gradient is created across the width of the anti-deflection plate. With the higher temperature of the temperature ygradient along the inner edge of each anti-deflection plate 50, the temperature gradient ytends to bow the anti-deflection plate inwardly in opposition to the outwardly bowing Itendency of the corresponding side plate 22. In some practices of the invention the anti-deflection plates 50 `are of such dimension in width and thickness that this natural temperature gradient in each anti-deflec- -tion plate sumces for completely counteracting the outward bowing tendency of the corresponding side plate. In this particular embodiment of the invention, however, means is provided to modify the inherent ytemperature gradient in each of the anti-deflection plates 50.

In the construction shown, the ltemperature along the inner dege Vof each of the anti-deflection plates 50 may be modified by directing cooling fiuid through a tube 54 and the temperature at the outer edge of the anti-deflection plate may be modified either by a cooling means 55 or a heating means 56. `It is apparent that the temperautre differential in an anti-defiection plate Sil may be increased by using only the cooling means 5S to lower the temperature along the outer margin of' the anti-deflection plate and that the vtemperature gradient may be decreased by introducing cooling fluid into the tube 54 along the inner edge of the anti-deection plate or by energizing the heating means 56 at the outer edge of the plate or, if necessary, by intnoducing cooling fluid into the tube 54 and simultaneously energizing the heating means 56.

As best shown in FIGS. 5 and 6, the upper outer edge of each of the side plates 22 may be chamfered to form an inclined surface 58 and the tube 54 may be of square cross sectional configuration to provide a substantial area of the tube in face to face contact with the inclined surface. The tube 54 may be releasably secured in place by a series of clamping bars 60 of the construction shown in FIG. 5. Each clamping bar 60 is formed with a longitudinal slot 62 to receive a cap screw 64 for adjustably anchoring the clamping bar to the underside of the corresponding anti-deflection plate 50. The inner end of the clamping bar 60 is formed with a V-shaped groove 65 that conforms with the square configuration of the cooling tube 54.

A suitable cooling fluid, which may be water, is fed to each of the cooling tubes 54 at a central point thereof by a supply pipe 66, the flow through the two supply pipes being controlled by corresponding manually operable valves 68 shown in FIGS. 8 and 9. The two opposite ends of each cooling tube 54 may discharge into the atmosphere but preferably are connected to discharge pipes 50, which discharge pipes may lead to a sewer. Usually water introduced into the tube 54 from the supply pipe 66 turns to steam which escapes through the discharge pipes 7l).

It is apparent that since a square cooling tube 54 makes only edgewise contact with the corresponding overlying anti-deflection plate 5t) but makes face contact with the corresponding side plate 2.2, the uid in the cooling tube has greater direct cooling effect on the side plate than on the anti-deflection plate. It is also apparent, however, that the effect of the cooling fluid in the tube 54 is to lower the temperature of the inner edge of the anti-deection plate to serve the purpose of the invention.

The cooling means 55 at the outer edge of each of the anti-deection plates 50 may be in the form of a heavy bar mounted in abutment against the outer edge surface of the anti-deflection plate. A zig-zag fluid passage 74 is formed in the bar 55 for flow of water in opposite directions from a central feed pipe 75 to two discharge pipes 76 which discharge pipes may be connected to a sewer. Flow through the two feed pipes 75 may be controlled by corresponding valves 77 shown in FlGS. 8 and 9.

To form the zig-zag fluid passage 74, spaced short bores 7S are formed in one edge of the bar 55 and then intersecting diagonal bores 80 are bored from the short bores. Three of the short bores 78 are used for connections with the feed pipes 75 and 7S, the remaining short bores being closed by suitable plugs 82.

The previously mentioned heating means 56 is in the form of a heating element mounted on the outer face of the corresponding bar 55. The heating element S6 is energized by suitable leads S and 86.

It is apparent that the provision of the cooling tubes 54 together with the cooling means 55 and the heating means S6 makes it possible to vary the temperature gradient across the two anti-deilection plates 59 in whatever manner is required for completely counteracting the tendency of the side plates 22 to bow outward. Thus the invention makes it possible to produce a plastic sheet S that is of uniform configuration with precisely parallel and precisely planar opposite faces.

In one practice of the invention, for example, a slight amount of cooling water is continuously introduced into the two cooling tubes 54 to lower the temperature along the inner edges of the two anti-deection plates 56 to control the upper value of the temperature differential and simultaneously the two heating elements 56 are suitably energized to raise the temperature of the outer edges of the two anti-deflection plates. It has been found that in such an arrangement the temperature gradient across each of the anti-deflection plates may be controlled readily and precisely by controlling the amount of current owing through the heating elements 56. For this purpose means may be provided to sense the temperature differential and means may be provided to vary the current that is supplied to the heating elements S6. Such an arrangement illustrated by FIGS. 6 and 8 will now be described.

As shown in FG. 6, the pressure differential in each of the anti-deflection plates Si) may be sensed by a central thermocouple $3 mounted in the anti-dellection plate near its inner edge and a second central thermocouple 9i) mounted in the anti-deflection plate near its outer edge. As shown in FIG. 8, the four thermocouples 8S and gt) are connected to a multiple recording pyrometer 92 which indicates the four temperatures at the four thermocouples respectively.

One of the leads 85 of each of the heating elements 56 is connected to a suitable current source and the other lead S6 is connected to one end of a potentiometer coil 94. A wiper Contact 95 that is adjustable along the potentiometer coil is connected by a wire 96 to the second side of the current source. Thus the degree of energization of the two heating elements 56 may be controlled by manual adjustment of the wiper contacts 95 and the cooling etfect of the cooling tubes S4 may be varied by adjusting the two corresponding valves 68.

A trial and error procedure may be followed to arrive at the particular temperature differentials required in the two anti-deflection plates 5l) when a given resin is forced through the passage 2t) under a given pressure and at given temperatures in the heating and cooling zones. In practice the temperature differential values are varied empirically until adjustments are found that produce a sheet of the desired accurate flat configuration. When the correct temperature differentials are found they are made of record for future use and whenever a production run is repeated the operator manipulates the valves 68 and the wiper contacts 95 as required to produce the desired temperature readings on the recording pyrometer 92.

FlG. 9 indicates how the same arrangement may be modified for automatic control. The automatic control requires means to sense outward bowing of the two side plates 22 of the passage structure. The sensing means, for example, may be a strain gage such as the Flexagage described in the October 10, 1960, issue of Product Engineering, pages 55 and 57. The Flexagage comprises two spaced parallel strain gages, one being close to the base metal to which the strain gage is cemented. FIG. 9 shows two such strain gages 98 mounted on the outer faces of the two side plates 22 respectively of the passage structure.

rl`he slightest tendency for a side plate 22 to bow outward results in the corresponding strain gage 98 sending a signal to an amplifier 160 and causes the amplifier to send a corresponding corrective signal to a servo motor 162. The servo motor 102 controls the wiper contact of a heating circuit of an anti-deflection plate 50 that is associated with the corresponding side plate 22. The heating circuit causes a temperature differential in the anti-deflection plate in the manner heretofore described to counteract completely the tendency of the side plate 22 to bow outward.

FIGS. l1() and 1d indicate how the force required to counteract the 4outward bowing tendency of the side plates 2,?. of the passage structure may be created hydraulically. On each side of the passage structure, ihydraulic uid under pressure is supplied to a hydraulic cylinder 104 through a pipe '105 from `a control valve 166. The control valve I106 is connected by a supply pipe 1% to a suitable source of pressurized liquid (not shown) and the control valve is also connected to a low pressure return pipe 11d. The hydraulic cylinder 104 has a hydraulic ram 112.

Each of the two hydraulic rams =1112y acts again-st a corresponding transverse pressure member 1114 that reinforces the corresponding side plate 22 of the passage structure. Each of the rams 'i12 straddles a strain gage 16.5 of the previously described type that senses any outward bowing of the corresponding pressure member. Signals from he strain gage are transmitted to an amplifier *116 which in turn sends corrective signals to a corresponding servo motor 11:8 that controls the corresponding control valve 1&6.

Our description .in specific detail of the selected embodimen-ts of the invention, will suggest various changes, substitutions and other departures from our disclosure within lthe spirit and scope of the appended claims.

We clm'm:

1. ln an apparatus wherein a passage formed by iixe walls including a relatively wide wall contines a mass of material under high pressure with consequent tendency for the wide wall to bow outward, the combination therewith of: a reinforcing member connected with said wall and extending transversely thereof; and means to create a temperature diiferential in said member with the higher temperature adjacent the wide wall whereby the rein-forcing member tends to bow inward to counteract the outward bowing tendency -of Ithe wide wall.

2. n an apparatus wherein a passage formed by xed walls including a relatively wide wall contines a mass of material under Ihigh pressure with consequent tendency for the wide wall to bow outward, the combination therewith of: means to sense outward bowing of said wide wall; and means responsive to said sensing means to apply inward force to the wide wall to counteract the outward bowing tendency thereof.

3. ln an apparatus wherein a passage formed by fixed walls including a relatively wide wall confines a mass of material under high pressure with consequent tendency for the wide wall to bow outward, the combination therewith of: a reinforcing member connected with said wall and extending transveresly thereof; means to sense outward bowing of said wide wall; and `means responsive to said sensing means to create a temperature differential across said reinforcing member with the higher temperature adjacent the wide wall to cause said member to tend to bow inward to counteract the outward bowing tendcncy of the wide wall.

4. In an apparatus wherein a passage formed by fixed walls including a relatively wide wall confines a mass of material under high pressure with consequent tendency for the wide wall to bow outward, the combination therewith of: means to sense outward bowing of said wide wall; hydraulic means to exert inward pressure on said wide wall to counteract the outward bowing tendency of the wide wall; and valve means 4responsive to said sensing eans to control said hydraulic means.

5. In an apparatus wherein a passage formed by fixed walls including a relatively wide wall confines a mass of material under high pressure with consequent tendency for the wide wall to bow outward, the combination therewith of: a reinforcing member connected with said wide wall and extending `transversely thereof; adjustable means to create a temperature differential in said reinforcing member with the higher temperature adjacent said wide wall whereby the reinforcing member tends to bow inward to counteract the outward bowing tendency of the wide wall; and means to sense and indicate said temperature differential for guidance in the adjustment of said means to create the temperature differential.

6, -In an apparatus wherein a passage structure having fixed walls including a relatively wide wall confines a mass of material under high pressure and heat is transferred to said mass through said wide wall with the consequent creation of a temperature differential through the thickness of the wide wall so that both said pressure and said temperature differential tend 4to cause the wide wall to bow outward, the combination therewith of: a metal reinforcing member connected to said wall structure and extending transversely of said wide wall, said reinforcing member being contiguous to said wide wall for reinforcement thereof and for heat transfer from the wide wall to the reinforcement member whereby the transferred heat creates an opposite temperature differential in the reinforcing member with the higher temperature adjacent the wide wall whereby the reinforcing member tends to bow inward to counteract the outward bowing tendency of the wide wall.

7. The combination as set forth in claim 6 which includes means to modify the temperature differential in said reinforcing member as required for substantially counterbalancing the loutwardly `bowing tendency yof the wide wall.

8. A combination las set forth in claim 7 in which said modifying means includes Imeans to cool a portion of said reinforcing member.

9. A combination as set forth in claim 7 which includes means to apply additional heat to a portion of said reinforcing member.

10. 1n an apparatus wherein fixed walls including a wide wall define a passage and a mass of material is forced through the passage under high pressure with consequent tendency for the wide wall to bow outwardly, the combination therewith of: a plate member positioned transversely of said wall substantially perpendicularly thereof with an inner marginal portion of the plate member overlapping a portion of the wide wall and attached to said portion of the wide wall; and means to create a temperature differential in said plate member with the higher temperature adjacent said wide wall whereby the plate member tends to bow inward to counteract the outwardly bowing tendency of the wide wall.

11, A method of reinforcing a fluid-confining wall against outward bowing of the wall by the pressure of the confined fluid, characterized by the steps of: placing a reinforcing member adjacent the outer side of the wall; and creating a temperature differential in said reinforcing member with the higher temperature adjacent said wall to create a tendency for the reinforcing `member to bow i11- ward to counteract the outward bowing tendency of the wall.

12 A method of reinforcing a fluid-confining wall against outward Abowing of the wall by the pressure of the confined fluid, characterized by the steps of: placing a reinforcing member adjacent the outer side of the wall; sensing outward bowing of the wall; creating a temperature differential in said reinforcing member with the higher temperature adjacent the wall to create a tendency for the reinforcing member to bow inward to counteract the outward bowing tendency of the wall; :and varying the temperature differential in accord with the sensed outward bowing of the wall.

13. A combination as set yforth in claim 2, in which said sensing means comprises at least one strain gauge secured to said wide wall.

References Cited in the file of this patent UNITED STATES PATENTS 2,017,553 Troiel Oct. 15, 1935 2,050,257 Bemis Aug. 11, 1936 2,084,113 Sherts June 15, 1937 2,126,869 Burchenal et el Aug. 16, 1938 2,168,889 Thomas Aug. 8, 1939 2,365,326 Bailey Dec. 19, 1944 2,713,188 Garvey July 19, 1955 2,736,064 Rubin Feb. 28, 1956 2,740,157 McCurdy et al. Apr. 3, 1956 2,765,492 Velvel Oct. 9, 1956 2,844,845 Krall July 29, 1958 2,859,503 Hennig Nov. 1l, 1958 FOREIGN PATENTS 167,559 Australia Apr. 26, 1956 

1. IN AN APPARATUS WHEREIN A PASSAGE FORMED BY FIXED WALLS INCLUSILNG A RELATIVELY WIDE WALL CONFINES A MASS OF MATERIAL UNDER HIGH PRESSURE WITH CONSEQUENT TENDENCY FOR THE WIDE WALL TO BOW OUTWARD, THE COMBINATION THEREWITH OF: A REINFORCING MEMBERS CONNECTED WITH SAID WALL AND EXTENDING TRANSVERSELY THEREOF; AND MEANS TO CREATE A TEMPERATURE DIFFERENTAIL IN SAID MEMBER WITH THE HIGHER TEMPERATURE ADJACENT THE WIDE WALL WHEREBY THE REINFORCING MEMBER TENDS TO BOW INWARD TO COUNTERACT THE OUTWARD BOWING TENDENCY OF THE WIDE WALL. 